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Full text of "dec :: dectape :: DEC-00-HZTA-D TU55 May69"

INSTRUCTION MANUAL 




DECtape 55 



DIGITAL EQUIPMENT CORPORATION • MAYNARD. MASSACHUSETTS 



DEC-OO-HZTA-D 




DECtape 55 

INSTRUCTION MANUAL 



September 1968 



DIGITAL EQUIPMENT CORPORATION • MAYNARD. MASSACHUSETTS 



1st Printing November 1966 
2nd Printing February 1967 
3rd Printing June 1967 
4th Printing October 1968 
5th Printing November 1968 
6th Printing May 1969 



Copyright (C) 1969 by Digital Equipment Corporation 



Instruction times, operating speeds and the like are in- 
cluded in this manual for reference only; they are not to 
be taken as specifications. 



The following are registered trademarks of Digital 
Equipment Corporation, Maynard, Massachusetts: 



DEC 


PDP 


FLIP CHIP 


FOCAL 


DIGITAL 


COMPUTER LAB 



CONTENTS 



CHAPTER 1 
INTRODUCTION AND DESCRIPTION 



Page 



1.1 General Description 1-1 

1.2 Scope of Manual 1-2 

1.3 Pertinent Documents 1-2 

1.3.1 Manuals 1-2 

1.3.2 Engineering Drawings 1-2 

1.3.3 New Module News Bulletins 1-3 

1.4 Functional Description 1-3 

1.5 Physical Description 1-4 
1.5.1 Electrical Details 1-6 

1.6 TU55 Performance Characteristics 1-9 

CHAPTER 2 
THEORY OF OPERATION 

2.1 Block Diagram Analysis 2-1 

2.2 Detailed Descriptions 2-4 

2.2.1 Interface 2-4 

2.2.2 Unit Select Lines 2-5 

2.2.3 Command Lines 2-5 

2.2.4 WRITE ENABLE Signal 2-5 

2.2.5 Interface Connections 2-6 

2.2.6 Read/Write Head 2-6 

2.2.7 Tape Motion Control 2-6 

2.2.8 Remote or Programmed Control 2-6 

2.2.9 Local (Manual) Control 2-7 

2.2.10 Motor Control 2-7 

2.2.11 Transport Selected Signal 2-8 

2.3 Module Descriptions 2-9 

2.3.1 Type R303 Integrating One Shot (Delay) 2-9 

2.3.2 Type W513 Level Amplifier 2-10 

2.3.3 Type G850 SCR Motor Driver 2-11 



CONTENTS (Cont) 







CHAPTER 3 






OPERATION 


3.1 


Introduction 




3.2 


Controls and Indicators 




3.2.1 


Operating Notes 




3.3 


Loading Tape 


CHAPTER 4 
MAINTENANCE 



4.1 

4.2 

4.2.1 

4.2.2 

4.3 

4.4 

4.5 

4.6 

4.7 

4.8 



5.1 

5.2 

5.3 

5.3.1 

5.3.2 

5.4 



1-1 
1-2 
1-3 
1-4 



Equipment Required 
Preventive Maintenance 

Weekly Schedule 

Monthly Schedule 
Tape Tension and Transport Stop Adjustment 
Head Output Check 
Head-Skew Check 
Write Enable Circuit Check 
Troubleshooting 
Recommended Spare 

CHAPTER 5 
ENGINEERING DRAWINGS 

Introduction 
Circuit Symbols 
Logic Signal Symbols 

Logic Levels 

FLIP CHIP Pulses 
Semiconductor Substitution 

ILLUSTRATIONS 

Type TU55 DEC tape Transport 

Hub and Reel Assembly 

Arrangement of DECtape Head 

Type TU55 DECtape Transport, Rear View 



Page 



3-1 
3-1 
3-1 
3-1 



4-1 
4-1 
4-1 
4-2 
4-2 
4-3 
4-4 
4-5 
4-6 
4-7 



5-1 
5-1 
5-1 
5-1 
5-1 
5-4 



1-1 
1-5 
1-6 
1-7 



ILLUSTRATIONS (Cont) 

Page 

1-5 TU55 Interface Connections 1-8 

2-1 DECtape Transport TU55 Block Diagram 2-1 

2-2 Head Connections 2-4 

2-3 Schematic of R303 Integrating One-Shot 2-10 

2-4 Schematic of G850 SCR Motor Drive 2-1 1 

4-1 Module Adjustment Trimports 4-3 

5-1 DEC Symbols 5-2 

5-2 FLIP CHIP R-Series Pulse 5-4 

5-3 FLIP CHIP B-Series Pulse 5-4 

Module Schematics 

Solid State DECtape Transport, TU55-0-2 5-5 

Module Utilization List, TU55-0-5 5-7 

Bus Bar for TU55, TU55-0-4 5-7 

Relay, G851 5-8 

Diode Cluster, R002 5-8 

Inverter, R107 5-9 

Diode Gate, Rill 5-9 

Dual Flip-Flop, R202 5-10 

Integrating One-Shot, R303 5-10 

Solenoid Driver, W040 5-11 

Level Amplifier, W513 5-11 

TABLES 

1-1 Summary of Equipment Characteristics for the TU55 DECtape Transport 1-9 

2-1 Motor and Brake Operation Truth Table 2-9 

3-1 Functions of Controls and Indicators 3-2 

4-1 Recommended Maintenance Equipment 4-1 

4-2 Recommended Spare Parts 4-7 

5-1 Semiconductor Substitution 5-4 



CHAPTER 1 
INTRODUCTION AND DESCRIPTION 



1.1 



GENERAL DESCRIPTION 



The Type TU55 DECtape Transport (see figure 1-1) is a solid-state, bidirectional, magnetic- 
tape handlingdevice designed and manufactured by the Digital Equipment Corporation (DEC) for use in 
DEC digital computer systems. When used with a suitable DECtape control system, the 11)55 provides a 
fixed-address magnetic-tape facility for high-speed loading, readout, and program updating. The DEC- 
tape control system directs the transport to read forward or in reverse, to write forward or in reverse, to 
stop, and to go. The TU55 contains tape handling elements, drive mechanisms, and solid-state switching 
circuits which switch the tape head onto a master bus system and interpret command instructions from the 
control unit. The highly reliable solid-state switching circuits in the TU55 are completely compatible 
with the Type 555 DECtape Transport (which uses relay switching) and may be used to modify and 
expand systems employing this type of transport. 




* ,V 



Figure 1-1 Type TU55 DECtape Transport 
1-1 



1.2 SCOPE OF MANUAL 

This instruction manual is intended to aid personnel in the maintenance of the 11)55 DECtape 
Transport. The equipment is discussed primarily from a maintenance point of view, but some information 
is given on the operation of its associated controls and indicators. The documents listed below provide 
operational information required for programming. 

Since the transport is one element of a computer/control/transport system, the reader should 
know the basic internal operations of both the computer and control . Of special importance are the 
sections concerning program interrupts, programmed in/out transfers, and the databreak facility in the 
computer; and the select and motion control logic in the external DECtape control. Detailed descrip- 
tions of the tape format, instruction repertoire, and programming practice for using the TU55 with a 
particular computer is described in the user handbook for the computer. Control information for the 
TU55 can be obtained from the maintenance manual for the DECtape control system used with the 
transport . 

1 .3 PERTINENT DOCUMENTS 

The following documents provide source information relative to the use of the DECtape Trans- 
port Type TU55. 

1.3.1 Manuals 

Digital FLIP CHIP Modules Catalog, C-l 05 

PDP-7 User Handbook, F-75 

PDP-8 User Handbook, F-85 

DECtape Control 550 Instruction Manual, H-550 

DECtape Control 551 Instruction Manual, H-551 

DECtape Control 552 Instruction Manual, H-552 

DECtape Control TC01 Instruction Manual, DEC-08-I3AB-D 

DECtape PDP-8 Programming Manual, Digital-8-27-U 

1 .3.2 Engineering Drawings 

A set of reduced engineering drawings for the TU55 is contained in chapter 5. These drawings 
are in addition to the complete set of full-size drawings forwarded with each TU55. As explained in 
chapter 5 all maintenance personnel should use only the full size engineering drawings for work on the 
equipment because these drawings show variations peculiar to an individual installation. 



1-2 



1 .3.3 New Module News Bulletins 

G850 SCR Motor Driver 

G851 Relay 

W513 Level Amplifier 

In addition to the above documents, complete sets of Library Programs are available for each 
computer using DECtape systems. 

1 .4 FUNCTIONAL DESCRIPTION 

The TU55 Transport provides a read/write head for recording and playback of information on 
five channels of the 0.75-inch tape. Each channel consists of two nonadjacent coils which are wired 
in series. Thus, information on one track combines with redundant information on another to create a 
single signal. Connections from the read/write head are made directly to the external control unit which 
contains the read and write amplifiers as well as the command logic for the selection and remote control 
of tape motion. 

The left half of the front panel (see Figure 1-1) contains the tape deck with reels and reel 
motors, tape guides, and the read/write head; the right half is the local control panel with rocker 
switches for selection and manual operation. The 600-rpm induction motors that drive the reel hubs 
directly control tape motion. No capstans, pinch rollers, or drag pads contact the tape. 

The logic circuits of the TU55 command tape movement in either direction over the read/write 
heads. Solid-state switching circuits completely control the tape drive motors. These circuits govern 
the torque applied to each reel motor to transport the tape across the head in accordance with specific 
commands (i.e., go, forward, reverse, stop). 

In normal tape movement, full torque is applied to the take-up reel, thus establishing the 
direction of motion. Reduced torque, applied to the trailing reel, maintains proper tape tension. Tape 
motion is bidirectional so that either reel can serve as the take-up reel. The DECtape system uses the 
so-called Manchester phase recording technique rather than an amplitude sensing technique; thus, tape 
speed need not be a precisely controlled parameter. Actually, the speed varies ±20%, depending upon 
the diameter of the tape pack on the take-up reel . An electromagnetic brake mounted on each motor 
shaft achieves a positive stop by braking the trailing reel at the end of a motion command. The take-up 
reel motor continues to apply partial torque to take up tape slack. Whenever the tape is motionless, 
one of the two reel brakes is applied opposite to the direction of the last tape movement. 



1-3 



Tape movement is controlled either by commands originating in the computer and applied to 
the TU55 via a suitable DECtape control system, or by commands generated through manual operation 
of rocker type switches located on the front panel of the transport. Typical DECtape control systems 
which allow transfer of information between the computer and the TU55 are as follows: 

Computer Typical DECtape Control System 

PDP-1, -4 and -7 Type 550 

PDP-6 Type 551 

PDP-5 and -8 Type 552 

PDP-8 TC01 

PDP-9 TC02 

Manual control is used to mount new reels of tape on the TU55 or as a quick maintenance check for 
proper operation of the control logic in moving the tape. 

External DECtape control systems may control up to eight individually addressed TU55s to 
read or write tape. The operator may select the address of each drive by adjusting the thumbwheel 
selector at the center of the TU55 local control panel (see figure 1-1). The operator may also place 
the drive off-line by a setting on the same thumbwheel or by switching the drive for local operation. 
In local operation, the head is disconnected and the rocker switches on the local control panel regu- 
late tape motion . 

1 .5 PHYSICAL DESCRIPTION 

All components of the TU55 are mounted on a preformed and assembled chassis. Roller slides 
that allow easy access to the top, sides, and rear of the drive hold the chassis in a standard DEC bay. 
Double doors in the front and rear are held closed by magnetic latches. Power supplies and controls 
are mounted on the rear of the DEC bay. Generally, the transport is mounted with others in the same 
bay that contains the DECtape control system. 

The tape deck is machined from 3/8-inch cast aluminum plate and held to the chassis by cap 
screws at the corners. Reel motors, tape guides and the head are secured only to the deck. This 
arrangement preserves the integrity of the tape alignment by the rigidity of the deck plate. Heavy 
extruded aluminum plates at the top and bottom front of the chassis serve as bumpers to protect the 
deck and control panel. The head is mounted in direct contact with the deck and is secured at both 
sides by brackets. Head azimuth is set during manufacture of the drive and cannot be adjusted in the 
field. 



1-4 



CAUTION 

No attempt should be made to loosen the brackets and change the head 
position. 



Reel motors are held by four cap screws (hidden by the reel hubs) from the front of the deck. 
At the rear of the shaft (which extends from both ends) is the electromagnetic brake. At the front, the 
shaft has a flat for securing the reel hub by a single Allen-head set screw. The hubs are flanged qt the 
rear and have an annular spring resting in a slot cut into the reel circumference. Beneath the spring in 
the slot is a rubber ring seal which causes the spring to protrude above the slot to secure the reel (see 
figure 1-2). The reel is a 1 -piece mold of phenolic composition. The inside circumference at the back 
of the reel fits the hub. In front, however, the inside circumference is slightly larger, allowing the 
hub spring to expand outward and to secure the reel. The clearance between the rear of the reel hub 
and the tape deck is nominally 15 mils, but may vary on individual machines to guarantee proper tape 
alignment in the guides. The guides are machined from aluminum and have a curvature designed to 
maintain air-film lubrication between the tape and guides as long as tape is in motion. A fan mounted 
on the top chassis plate continuously blows cooling air over the reel motors. 




RING SEAL 



DECK PLATE 



Figure 1-2 Hub and Reel Assembly 
1-.5 



The redundantly paired tracks that form the five channels on the head are illustrated sche- 
matically in figure 1-3. Three track pairs are used for data; the remaining pairs are used as timing and 
control information. The two timing tracks are on the outside at opposite sides of the tape. Just inside 
these are the two tracks for the mark channel, the contents of which signify to the external control the 
type of information in the data channels. The six tracks for these data channels are grouped at the 
center, where they are least affected by skew. Since writing may take place in the data channels 
while reading takes place simultaneously in the timing and mark channels, the tracks for the latter 
channels are separated slightly from the data channel tracks to allow room for additional shielding. 



TAPE 
DECK 
PLATE 



STANOARO 
SPACING 

.073" 



r 



TAPE 
WIDTH - 
0.750" 



AUGMENTED 

SPACING 

.088" 



HH H 



1 



_l _ 


DAT/ 
CHA 


Sr 


























i 

DATA 
CHAN 








2 


DATA 
CHAN 








3 
MAR 


K CHANNEL 








TIMING CHANNEL 







Figure 1 -3 Arrangement of DECtape Head 



1.5.1 



Electrical Details 



The TU55 requires the DEC standard +10 and -15 vdc power levels at the terminal-tab con- 
nectors on the rear panel (figure 1-4). These dc levels are normally provided from power supplies 
associated with the DECtape control system. AC power (105-125v, 60 cps) is connected at the 3- 
terminal receptacle on the rear panel. 



1-6 




Figure 1-4 Type TU55 DECtape Transport, Rear View 

Signal connections to and from the DECtape control system are made through 18-pin and 
36-pin FLIP CHIP cable terminators that plug directly into the module mounting panel on the rear 
panel (Figure 1-4). Cable locations in this mounting panel are shown in Figure 1-5 with respect to the 
other installed modules. The command cable terminator is a Type W023 18-Pin Connector for the logic 
signals governing selection and tape motion. The head signal connector is a double-size Type W032 
36-Bit Connector for shielded cable. Two sockets at the TU55 logic panel are reserved for the command 
connector and two for the information connector. The pins for each pair are bussed together. This is 
done so that TU55s may be grouped. Each TU55 receives its information and commands from one trans- 
port in the group through one set of connectors and sends these to the next transport through another set 
of connectors. 

The writing current is 210 ma. Playback peak-to-peak channel voltage is between 10 and 
12 mv when the tape is up to speed. 



1-7 









G 
850 


G 
850 













R 
002 


W 
040 







(to 



z z 

5 ° 







< 






IT 




H 




O 








z 


<z 




o 


? 




o 




u 





R 
303 





































w 

040 


R 
107 


R 
111 


R 
111 


R 
202 


W513 

OR 
W990 


R 
111 


R 
701 


R 
303 





















?p 



=>9 

o w 



Figure 1-5 TU55 Interface Connections 

Command signal levels from the DECtape control to the TU55 Transport are either ground or 
-3v. (Equivalent signals to a 555 Transport are either -3 or -15v.) For existing systems with a con- 
trol system for the 555 Transport, exchanging a single FLIP CHIP module (a W513 Level Amplifier when 
the 11)55 Transport is connected to a control designed to drive relay Transport 555; otherwise a W990 
Blank Module) allows the TU55 to accept command signals of either type. 

The reel brakes and the head relay are energized by — 15v through special solenoid driver 
circuits; the motors are controlled by silicon controlled rectifier (SCR) circuits that phase-switch the 
1 10 vac line power. 

The TU55 uses twelve types of FLIP CHIP logic modules (connectors excluded) as follows: 



Amplifier 



2 W040 Solenoid Driver 

1 W513 Level Amplifier/W990 Level 

1 R107 Inverter 

4 Rill Diode Gate 

1 R303 Integrating One -Shot 

1 R002 Diode Network 



2 R202 Dual Flip-Flop 

1 R303 Integrating Delay 

2 G850 SCR Motor Driver 
1 G851 Relay Module 

3 W023 Indicator Amplifier 
1 W701 Input Network 



All modules are mounted on a dip-soldered epoxy board with 18 gold-plated contacts at one 
end (36 on double-height modules) for connection to the mounting panel receptacle, and a plastic handle 
bearing the type number at the other end. Three contacts on each module are reserved for supply voltages: 
A and B supply the +10 and -15v standard power levels; C is the ground. 



1-8 



1 .6 TU55 PERFORMANCE CHARACTERISTICS 

A summary of the characteristics of the 11)55 equipment is given in table 1-1 . 



TABLE 1-1 SUMMARY OF EQUIPMENT CHARACTERISTICS 
FOR THE TU55 DECTAPE TRANSPORT 



Overall Size 
Mounting 



Power Requirements 



Connectors 



Cooling 

Operating Temperature 

Humidity 



Ge neral 

10-1/2 in. high, 19-1/2 in. wide, 9-3/4 in. deep 

Standard 19-in. rack. Four ^1 0-32 screws mount chassis 
track assembly which holds transport. 

Chassis can be extended 16-3/4 in. beyond mounting 
surface for maintenance 

— 15 vdc, 1 .0 amp maximum 

+ 10 vdc, 50 ma maximum 

1 15 vac ±10%, 1 .0 amp idle, 2.0 amp maximum current 

(60- and 50-cycle models) 

Commands: two I8-terminal FLIP CHIP female 
connectors 

Information: two 36-terminal FLIP CHIP female 
connectors 

Internally mounted fan 

50 to 110°F ambient 

10 to 90% relative humidity 



NOTE: The manufacturer of the magnetic tape for DECtape recommends 40 
to 60% relative humidity and 60 to 80°F as acceptable for operating environ- 
ment. 



Capacity 
Reel Diameter 
Reel Diameter Ratio 



Tape Characteristics 
260 ft of 3/4 in., 1 mil thick Mylar sandwich tape 
2-3/4 in. empty reel, 3-3/4 in. for 260 ft of tape 
Approx,. 1:4 (maximum to minimum) 



1-9 



TABLE 1-1 SUMMARY OF EQUIPMENT CHARACTERISTICS 
FOR THE TU55 DECTAPE TRANSPORT (continued) 



Tape Handling 

Speed 

Density 

Information Capacity 

Tape Motion 



Tape Characteristics (continued) 

Direct drive hubs and specially designed guides which 
float the tape over the head hydrodynamically . No 
capstans or pinch rollers are used. 

93 ±12 ips 

350 ±55 bits per inch 

2.7 x 10 bits per reel assembled into computer-length 
words by external DEC tape control 

Bidirectional 



Times given are for 90% full speed. 

Start Time 
Stop Time 
Turn Around Time 



Drive Characteristics 



<1 50 msec 
<1 50 msec 
<250 msec 



Commands* 



Unit Select* 



Input Signals to Transport from Control 

forward! 



REVERSE J 




/ground level assertion, 

y normally complementary levels 

f ground level assertion, 

y normally complementary levels 

negative level assertion used to stop 
transport when computer halts 



SELECT 1 through SELECT 8 (the selected line will 

be at ground) 



Control 



Ou tput Signal from Transport to Control 

WRITE ENABLE (standard DEC ground level assertion) 



*Valid only when the control is operating the solid-state Transport TU55. When relay type transport 
(Type 555) signals are received a conversion is made to DEC standard levels by the W513 Level 
Amplifier which converts the — 3v level to ground and the floating input to — 3v. 



1-10 



CHAPTER 2 
THEORY OF OPERATION 



2.1 



BLOCK DIAGRAM ANALYSIS 



The TU55 logic is shown in the functional block diagram of figure 2-1 . All front panel con- 
trols and indicators are shown within the blocks representing the associated logic. The functions of these 
controls and indicators are summarized in table 3-1 . Diamonds indicate the direction of signal flow be- 
tween blocks; an open diamond represents a signal effective (asserted) at ground; a closed diamond rep- 
resents a signal asserted at — 3v. All interface signals are received from or transmitted to an external 
DECtape control system. One of the two connectors at the left of figure 2-1 serves as a command and 
information signal bus to other TU55s. 



•-o- 



A6 



WRITE ENABLE 



(8) 



SELECT 
LOGIC 



SELECT 

♦ ♦ 



SELECTED 



-o 



w 



WRITE 
ENABLED 

B 

WRITE 
LOCK 



DELAY ( 1 ) 
DELAY (0) 

MOTION (0) 



BB-EI 



MOTION 
CONTROL 



DIRECTION ( 1 ) 



MOTION (I) 



DIRECTION (0) 



AB2 


AB3 




(SELECTED 






HEAD 
RELAY 










^TMG (4) 










HEAD 


_J"MG (4) 








MRK (4) 


MRK (4) 








DATA t (4) 


DATA 1 (4) 








DATA 2 (4) 


DATA 2(4) 








^DATA 3 (4) 


DATA 3(4) 


\y 




<^J 















DELAY (0). 



fE 



DELAY ( 1 K 



RIGHT BRAKE 



AND I — , I ♦£ 1 



-c 



GO 
REV 



OR 



-* — ♦ 



HEET 



LEFT BRAKE 



STOP TORQUE 



FULL TORQUE, 



DRAG TORQUE, 



RIGHT 
MOTOR 
DRIVER 



DRAG TORQUE, 



FULL TORQUE 



STOP TORQUE, 



LEFT 
MOTOR 
DRIVER 





RIGHT 

LEFT 
REEL, 



NOTE: An arrow signifies a nonstandard DEC signal, such as motor voltage, 
head playback, brake voltage, etc. 

In the motion control block the arrow above a switch means that pressing this 
switch results in tape movement in the indicated direction when the middle 
switch is in the LOCAL position. 

Figure 2-1 DECtape Transport TU55 Block Diagram 



2-1 



The SELECTOR LOGIC block in figure 2-1 includes the front panel thumbwheel selector 
shown in figure 1-1 . This selector has nine positions (designated 1 through 8 and OFF LINE) for selecting 
one of eight select lines which are the outputs of a binary-coded-decimal decoder in the external DEC- 
tape control system. During addressing, only one of the eight input select lines is at the asserted 
ground. In remote operation, the SELECT output is asserted negative whenever the thumbwheel setting 
corresponds to the asserted address line from the DECtape control system. 

Writing is possible on a selected drive only when that drive furnishes control with a WRITE 
ENABLE signal at ground. A selected TU55 furnishes such a signal when the WRITE ENABLE switch in 
figure 2-1 is on. When this switch is set to WRITE LOCK, the output line is negative and writing can- 
not take place. If the control is commanded to perform a write function when WRITE LOCK is selected, 
it displays a selection error flag to notify the program of the mistake. 

The five motion commands from the external DECtape control system are shown entering at 
the left center. The ALL HALT signal is asserted negative by the external control whenever the computer 
program execution is halted either by the program or by the operator. When the program is halted, the 
computer cannot issue commands to peripheral equipment. The ALL HALT signal stops those transports 
that were in motion at the time of the ALL HALT command, thus preventing a complete run-off of the 
tape . 

The other four commands, GO, STOP, FORWARD, and REVERSE, are asserted at ground by 
the external control in response to computer program commands. In current DECtape controls, GO and 
STOP are complementary levels. In the following discussion, the GO, STOP, FORWARD, and REVERSE 
lines referred to are at the output of the signal interface module (B07). 

Tape motion begins at a selected TU55 when the GO line is asserted (STOP must be held 
false throughout the desired interval of tape motion). Motion stops whenever the STOP line is asserted 
while the GO line is simultaneously held false. 

The same conditions as above apply to the FORWARD and REVERSE lines. For a selected 
transport which is set to REMOTE, asserting the FORWARD line (while holding the REVERSE line false) 
causes all subsequent remote GO commands to move tape forward. Similarly, asserting the REVERSE 
line (while holding the FORWARD line false) selects the reverse direction. In LOCAL operation, the 
reverse and forward tape-motion switches override the last REMOTE direction command so that the tape 
always moves in the direction of the arrow above the switch (see figure 2-1). 

Current DECtape controls generate the GO/STOP and the FORWARD/REVERSE signals as 
complementary levels. Forward tape motion, for example, is commanded by assertion levels on GO and 
FORWARD accompanied by false levels on STOP and REVERSE. 

When forward motion is commanded either locally or remotely, the motion control logic asserts 
the FWD output negative. This signal releases both brakes and applies full clockwise torque to the right 



2-2 



motor and partial counterclockwise torque to the left motor. As a result the tape moves from the left 
reel across the head onto the right reel. The REV line (asserted negative in response to the REVERSE 
motion command) applies full torque to the left motor, partial torque to the right motor, and simulta- 
neously releases both brakes. Tape motion, therefore, is from right to left. At the end of either com- 
mand, the STOP line is asserted negative and triggers the stop delay (about TOO msec). For the 
duration of the delay, full torque is applied to the trailing motor and stop torque is applied to the 
leading motor (see section 3.3). Thus, for the duration of the delay after the STOP command has 
been issued, the motor torques are reversed causing tape movement also to be reversed. This time, 
however, is very short and when the delay times out, the motors come to zero speed while changing 
their rotation from one direction to the other. After the STOP DELAY times out, the tape becomes 
motionless and partial torque is applied to both reels to take up the tape slack and the brake is applied 
to the motor shaft which was trailing during the previous motion. The effect of the delay is nullified 
if a new motion command is given before the end of the 1-sec interval. Then, the torque signals to the 
left and right motor drives are immediately reestablished according to the new motion command. The 
delay starts again at the leading edge of each STOP signal regardless of the frequency of its occurrence; 
i.e., no recovery time is inherent in this type at delay. 

An illustration of the tape head is shown in figure 2-2. Every channel consists of two tracks 
associated with their coils. When writing, the current flows from ground (center tap) through one of 
the coils (to either + or — terminal)to saturate the tape in one direction and through the other coil to 
saturate the tape in the other direction. The coils for the two tracks are wired in series and are brought 
out as four lines: ground, +, — , and the shield. Within the head, relay module, the +, — , and ground 
lines (center taps) for a channel are switched by one of five 3-pole, normally open reed relays. Shields 
are not switched, but are through-connected from the head to the interface connectors. A separate 
line from the timing channel (also shown in figure 2-2) is brought out to allow measurements of head 
skew (or the head perpendicularity). This line isusedonly for test purposes (and not by the external 
control). The single head-ground line is used to ground the head case. 



2-3 



22 PIN 

AMPHENOL 

PLUG 









TRACK 3 


TRACK 6 


DATA 1 


TRACK 1 


TRACK 10 


- TIMING 


TRACK 4 


TRACK 7 


DATA 2 


TRACK 2 


TRACK 9 


-MARK 


TRACK 5 


TRACK 8 


DATA 3 


N S 


N S 




N S 


N S 






SKEW CENTER 
CHECK TAP 



- TIMING 
-MARK 




Figure 2-2 Head Connections 



2.2 



DETAILED DESCRIPTIONS 



This section describes, in detail, the flow of information and control through each of the 
functional elements of the TU55 control unit. The discussion is limited to describing the various 
modules as logical operators. Detailed descriptions of individual circuits are given in section 2.3, 
Module Descriptions. 

The basis for the discussion in the remainder of this section is the block schematic in DEC 
drawing BS-D-TU55-0-2. This drawing is subdivided into zones bounded by horizontal section A 
through D and vertical section 1 through 8. Circuit locations are referenced by a letter-numeral 
combination. For other drawing symbology, refer to the introductory paragraphs of chapter 5. 



2.2.1 



Interface 



All interface signals received or transmitted by the tape motion control circuits are trans- 
ferred between the TU55 and the external DECtape control system. Interface signals for the tape- 
motion control logic consist of: eight unit select input lines, five command input lines, and selected 
write enable output control lines. Bus connections for these signals from the DECtape control system 
fro the TU55 are made by plugging a FLIP CHIP cable connector into module receptacles (A5 or A6). 
These signals together with the power lines and the information lines (to be described under Read/Write 
Head Circuits) constitute the interface for the entire TU55. 



2-4 



2.2.2 Unit Select Lines 

The eight unit select lines, numbered 1 through 8, are the outputs of a binary-coded-decirnal 
decoder in the DECtape control and are supplied to the TU55 for application to the unit selector switch 
S5 (A7, A3). This manually operated switch establishes the programmed address of the TU55, to allow 
the TU55 to be addressed by the computer program. The unit select lines are connected directly to the 
corresponding numbered position contacts of the selector switch. The switch wiper arm is connected to 
input terminal R of the module B07 (C8), thus providing the SELECT command as an output at terminal 
B07. Module B07 is either a Type W513 Level Amplifier or a Type W990 Blank Module with appropriate 
jumpers, depending upon the type of input signals. As previously explained, when the input levels are 
— 3v and ground (i.e., the control has been designed specifically to drive the solid-state drive), the 
W990 Blank Module is used. When an older type control is used (such as 550, 551, or 552) the W513 
Level Amplifier is used instead to convert relay driving levels to DEC standard levels. The same applies 
also to the command line level. 

2.2.3 Command Lines 

The four ma|or command lines: GO, STOP, FWD, and REV set or clear the MOTION or 
DIRECTION flip-flops (C7, C6) based upon programmed commands from the computer. 

The ALL HALT command level is generated in the control logic of the computer and occurs 
when the program is halted. This negative level for assertion clears the MOTION flip-flop (C4) to the 
motion(O) state to stop motion of the transport when the computer program halts. Obviously when the 
computer program is halted, the computer connot Issue commands to peripheral equipment, and so this 
action is taken to prevent indefinite running of the transport and to prevent the tape from running off 
the reel. However, toenable the transport to run under local (or manual) mode, the ALL HALT level is 
ANDed with the remote level (C4). 

2.2.4 WRITE ENABLE Signal 

The TU55 generates the ground level WRITE ENABLE signal for routing to the DECtape con- 
trol from terminal board A5, pin L. To assert this level the WRITE ENABLE/WRITE LOCK switch S3 (A6) 
must be in the WRITE ENABLE (up) position. This position enables diode gate VUT of module Bl 1 (B6) 
to generate the WRITE ENABLE signal, and causes the lighting of the WRITE ENABLE indicator on the 
front panel. 

For the older type controls, the W513 Level Amplifier circuit serves as a protection diode 
for the R107 (B1 1 ) Inverter. 



2-5 



2.2.5 Interface Connections 

Information lines are brought to the read/write head from the DECtape control system where 
they are bussed together for connection to other transports. Connections to this bus from an individual 
TU55 are made by cable connections of module connectors (A4 and B4). These connections are wired to 
the Type G851 Relay Module (A4, B4) for connection to the read/write head when the relay is operated 
by the (SELECT) signal amplified by solenoid driver ER of the Type W040 Module (B4). 

2.2.6 Read/Write Head 

A type G851 Relay Module (A4, B4) establishes connection to the read/write head from the 
information bus lines of the DECtape control system. This module consists of 5 x 3 single-pole, normally 
open contacts which are closed when the relay is energized. The relay is energized when the TU55 is 
selected, thus connecting the read/write head channel coils to the control. 

2.2.7 Tape Motion Control 

Tape movement and direction of movement are controlled by two Type R202 Flip— Flops; namely, 
stop/go MOTION flip-flop (C6) and a reverse/forward DIRECTION flip-flop (C7). The flip-flops are 
set or cleared by command signals originating in the DECtape control system or in the reverse tape-motion 
and forward tape-motion switches on the front panel (see Figure 1-1). 

2.2.8 Remote or Programmed Control 



The four major commands that originate in the DECtape control system are GO, STOP, FOR- 
WARD, and REVERSE. Type Rill Diode Gates (B4, B5, B6) NAND-and combine these commands with 
the SELECT level within the TU55. The output of these gates is used to set and clear the MOTION and 
DIRECTION flip-flops. Therefore, motion and direction are controlled only in the selected transport. 
The TU55 receives these four major commands as direct connections from the DECtape control system. 
The eight unit select lines, designated 1 through 8, (B8) are connected to appropriate positions of the 
unit selector switch (A7, A8). The transport is selected when the selected line coincides with the 
position of the unit selector switch. The negative SELECT level is conditioned by LOCAL and SELECT 
ground levels (B7) if the transport is switched to the local mode. Then computer-control selection of 
the transport is not affected. 

The magnitude of the load on the address line is examined by the external control during 
selection to determine whether more than one DECtape transport is being addressed. 



2-6 



2.2.9 Local (Manual) Control 

Switches on the front panel of the TU55 provide for manual control of the tape motion. The 
shift in control from remote to local is performed through the REMOTE/OFF/LOCAL switch S2A (A6). 
With the switch on LOCAL, the selected level (C7) is forced to ground potential thus inhibiting the 
external command NAND gates (Rills). Inhibiting these gates prevents commands from the DECtape 
control system from affecting the state of either the MOTION or DIRECTION flip-flops and thus pre- 
vents interference with manual control. With switch S2 on LOCAL, +10v is supplied to both the 
REVERSE S4 (A5) and FORWARD SI (A7) switches. This condition permits the switch operation to es- 
tablish the appropriate state of both the MOTION and DIRECTION flip-flops when pressed. Switches 
SI and S4 are of the momentary contact type which return to a reset position when released. When the 
REVERSE switch is pressed, the MOTION flip-flop is set to the motion(l) state and the DIRECTION 
flip-flop is set to the direction(O) state by grounding the appropriate output connection terminals of the 
flip-flops. The grounding of the flip-flop outputs is done via the outputs of the W701 Switch Filter, 
generally used to interface switch action to the logic (refer to the circuit description). This module is 
used both to filter out switch contact bouncing and to load the same contact with some current from a 
sufficiently high potential to positively bridge across any insulating film that might be formed over the 
switch contacts, thus assuring an electrical contact when the switch is pressed. 

Under these conditions the tape moves in reverse. When the FORWARD switch is pressed, 
the MOTION flip-flop is set to motion(l) and the DIRECTION flip-flop is set to direction(l), moving 
the tape forward. Release of either the REVERSE or FORWARD switch clears the MOTION flip-flop, 
thus stopping tape motion. Therefore, tape motion under manual control occurs only as long as the 
REVERSE or FORWARD switch is held down physically. Inter-wiring between the REVERSE and FORWARD 
switches provides a protection feature, so that if both switches are pressed simultaneously, the FORWARD 
direction will prevail. 

2.2.10 Motor Control 

The two motors which move the tape past the read/write head are operated by ac power which 
is controlled separately for each motor by an SCR switch on a Type G850 SCR Motor Control Module 
(D4, C4). These SCR circuits, in turn, are controlled by combinations of the states of both the MOTION 
and DIRECTION flip-flops. A brake on the shaft of each motor is also individually controlled by com- 
binations of the state of these control flip-flops (C7, C6). The states of the control flip-flops are 
decoded by Rl 1 1 NAND gates which control the SCR circuits, and by Type W040 Solenoid Driver 
Modules (D4, C4) which control the brakes. Table 2-1 indicates the assertion levels (1) which operate 
the motors and brakes; or indicates the nonassertion levels (0) which do not operate these devices for 
all combinations of control flip-flop conditions. 

2-7 



Table 2-1 also presents the three states of motor and brake operation when the tape is 
running in either the forward or reverse direction. 

The functions of the Type G850 SCR Motor Driver Modules (D4, C4) are as follows: with a 
negative assertion level at terminal H, the motor is driven at full torque; with a negative assertion level 
at terminal F, the motor is driven with enough drag torque to take up slack in the tape when the motor 
functions as a trailing motor; with a negative assertion level at terminal E, the motor has just enough 
torque to take up slack in the STOP condition. 

When the tape is running in the forward direction, full torque is applied to the right motor 
and drag torque is applied to the left motor. When the STOP command is given, full torque is removed 
from the right motor and applied to the left motor for the duration of the delay of the Type R303 One 
Shot Module (07), and stop torque is applied to both motors. At the end of the one-shot delay, which 
is approximately 100 msec, full torque is removed from the left motor, the brake is applied to the left 
motor, and stop torque remains on both motors to take up the slack in the tape until the next command 
is received. (Of course the stop torque applied to that motor which has the brake on is doing nothing). 

A similar sequence of events occurs when tape movement is in the reverse direction and the 
STOP command is received. Hence, after a STOP command occurs, the brake is applied only to the 
shaft of the trailing motor, positively stopping the motor shaft to which it is applied. When the tape 
is at rest (which is most of the time), the stop torque applied to the motor to take up tape slack is 
minimum to avoid excessive heating of the system. 

The logical negative levels applied to pins E, F, and H of the G850 SCR Motor Control are 
ANDed with the negative BRAKE ENABLE level (C4, D4). This level is negative (B6) only when the 
REMOTE/OFF/LOCAL switch is on either REMOTE or LOCAL. When the switch is in the OFF position, 
the level is at ground potential and disables both the G850 SCR Motor Control motor circuits and the 
brakes (dc +10 and — 15v are still present). This switch position is used when a tape reel is to be 
mounted or dismounted and is also recommended when a particular drive is not being used. (On the 
older Type TU55 Transports the same 3-position switch was used to interrupt the ac power to the trans- 
port and the BRAKE ENABLE level did not condition the G850 circuit. Thus the power itself was 
interrupted instead of logically controlling the G850 Motor Control.) 

2.2.11 Transport Selected Signal 

The negative SELECT level enables another Relay Driver Type W040 (C7) whose output is 

sent through a resistor to interface pin K on A5/A6 modules from where it is sent to the control. The 

control can use this line to sense whether more than one transport is being selected at one time. Usually 

an analog type circuit uses the fact that current could go through the resistor when the relay (transport) 

is selected, and, if more than one (or no) transport is selected, causes an error signal. This feature is 
not needed when the transport is connected to a 550, 551 , or 552 Control . 

2-8 



Transformer Tl (C3) synchronizes the SCR firing with the 60-cycle waveform of the primary 
power. The Thyractor connected across the primary of this transformer protects the diode bridge rectifiers 
in the Type G850 Modules. 

Table 2-1 Motor and Brake Operation Truth Table 





Mode 


Control Eleme 


nt 


Left Motor 


Left 
Brake 


Right Motor 






S" 


rATES 


Pin H Pin F Pin E 


Pin H 


Pin F Pin E 


Right 


Operatior 


Direction 


Motion 


Delay 


Full 
Torque 


Drag 
Torque 


Stop 
Torque 


Full 
Torque 


Drag 
Torque 


Stop 
Torque 


Brake 




Running 





1 





1 








Off 





1 





Off 


Reverse 


Stopping 








1 








1 


Off 


1 





1 


Off 




Stopped 

















1 


Off 








1 


On 




Running 


1 


I 








1 





Off 


1 








Off 


Forward 


Stopping 


1 





1 


1 





1 


Off 








1 


Off 




Stopped 


1 














1 


On 








1 


Off 



2.3 



MODULE DESCRIPTIONS 



Complete circuit information for the FLIP CHIP modules in the Type TU55 DECtape Transport 
is contained in the replacement schematic engineering drawings (see chapter 5). A list of the FLIP CHIP 
modules used in the TU55 is included in engineering drawing PL-TU55-0-5, Module count list. Their 
locations are shown on drawing MU-TU55-0-5. These modules are described in DEC Digital FLIP CHIP 
Module Catalog, C-105, and in appropriate New Module News Bulletins. Descriptions of non-catalog 
modules are contained in the following subsections. 

2.3.1 Type R303 Integrating One Shot (Dela y) 

This module includes a zero-recovery-time multivibrator and complementary output buffers 
(see Figure 2-3 and DEC drawing RS-B-R303). It responds to inputs signals (up to 2 mc) which may occur 
at any time either within or outside the delay interval . Successive inputs above a preset frequency can 
postpone the delay indefinitely. 



2-9 




-i. X, X, X , X . X « 



R401 VARIABLE CLOCK 



Figure 2-3 Diagram of R303 Integrating One-Shot 



2.3.2 Type W513 Level Amplifier 

This module contains six identical level amplifier circuits (see engineering drawing RS-B- 
W513). The input levels are received from DEC relay or solenoid driver circuits having outputs which 
are between —2 and — 3v when the driver is "on"(1) and are floating when it is "off"(0). An input 
current exceeding 1 .2 ma to the level amplifier makes the input potential more positive than — 3.5v and 
asserts the output at ground. When the input current is cut off, the input potential returns to approxi- 
mately -5v and the output becomes — 3v. Since all circuits are identical, the first circuit in the re- 
placement schematic (input at D and output at E) is described. 

The circuit is quiescent when no input current is flowing into D. Diodes Dl and D2 clamp 
input return Rl at about — 5v. The drop across Dl maintains Q1 cutoff, thus allowing R3 to keep the 
Q2 base positive and cut off Q2. D4 clamps output E at the Q2 collector to -3v. 

When the input goes more positive to —2 to — 3v it startssupplying current to pin D. It will 
back bias Dl and turn on Ql . Q2 base current flows through Ql and R2 so Q2 turns on, bringing E to 
ground potential. When the input current at D opens, both transistors cut off again and the circuit is 
quiescent again. 

A resistor is tied to pin T. It is used to simulate relay currents such as those existing in the 
555 Relay Transport and therefore allows mixing TU55s and 555s in the same system. The current 
through this resistor is measured by an analog circuit at the control to determine whether one or more 
transports are being selected and causes an alarm or error signal in case the latter condition happens. 



2-10 



2.3.3 Type G850 SCR Motor Driver 

Essentially this module is an SCR switch for the ac voltage supplied to any one of the drive 
motors of the TU55. The SCR switch is turned on and off twice during each cycle of the ac power. The 
firing point of the SCR is controlled so that it can occur at almost any point along the sinusoidal wave- 
form of the ac power; thus controlling the amount of energy that is transmitted to the load (the motor), 
and thus achieving control of motor torque. A simplified schematic diagram of this module is shown in 
Figure 2-4, a complete schematic in DEC engineering drawing RS-B-G850. 




-3 A 'I 
H 

I- 

£ 



fULU 

Df^A6- 
5 TO PPjm o- 



Figure 2-4 Schematic of G850 SCR Motor Driver 

The SCR itself (D15), is connected into a diode bridge so that current always passes though it 
in the same direction (an SCR is not a bilateral device). The firing circuit for the SCR incorporates a 
unijunction transistor (Q4) and an RC timing network. The capacitor (CI) in this network starts to charge 
at the beginning of each half cycle of the ac voltage. When the voltage developed across the capacitor 
reaches the firing point of Q4, conduction starts and current flows in the primary of a coupling trans- 
former (Tl). Voltage induced in the secondary of Tl controls the firing of the SCR and causes the motor 
to operate . 

Three input timing circuits determine the trigger timing of the SCR. A -3V level applied to 
the two-diode input of these circuits cause the SCR to trigger at a fixed rate or a variable rate determined 
by the setting of potentiometers R5 and R9. The fixed input circuit (Q3) triggers the SCR near the 
beginning of the sinusoidal wave to produce maximum torque. 

A low voltage ac input is supplied to terminals U and V from the secondary at transformer Tl 
of the TU55 logic (not Tl of the module). This input voltage is full wave rectified and is clipped by a 



2-11 



Zener diode, but is not filtered. It provides the potential toward which the timing circuit attempts to 
charge. Being a stepped down version of the primary ac power which operates the drive motors, this 
voltage synchronizes the firing of the SCR to the line frequency. Since the voltage at the end of each 
half cycle is zero, the RC network must start charging at the end of each half cycle. Therefore, this 
pulsating voltage causes the SCR to fire each half cycle at a point in time measured from the zero 
voltage point. 



CAUTION 

Be very careful when handling this circuit or probing it for measurement 
purposes since it contains 115v ac. A short circuit caused by a probe 
could produce a high current. Do not tamper with this module without 
first disconnecting power from the back terminal. 



2-12 



CHAPTER 3 
OPERATION 



3.1 INTRODUCTION 

As stated in chapter 1 , the TU55 can be operated in either a local (manual) or a remote (auto- 
matic-programmed) mode. Local operation is accomplished by use of the controls and indicators on the 
front panel of the equipment. Remote operation is effected through programmed commands produced by 
the stored program of the computer. The following paragraphs contain information applicable to both 
modes of operation . 

3.2 CONTROLS AND INDICATORS 

The functions of the controls and indicators on the control panel in figure 1-1 are summarized 
In table 3-1 . Additional information of the action initiated by the controls is given in the following 
paragraph . 

3.2.1 Operating Notes 

When the REMOTE/OFF/LOCAL switch is in the OFF position, the REMOTE indicator does 
not light but the TU55 logic still responds to selection, control, and command signals from external con- 
trol . Consequently the external control may select and attempt to read or write tape but no tape motion 
takes place. In all normal modes, this condition idles both the DECtape control system and TU55 because 
no timing channel signal is made available from a motionless tape. When the system is commanded to 
write on the timing and mark channels, the timing pulses are generated within the external control per- 
mitting the control to operate as if tape motion were available. 

3.3 LOADING TAPE 

To mount a reel of DECtape on the TU55 after energizing the equipment, proceed as follows 
(see figure 1-1 and table 2-1): 

To load tape set the REMOTE/OFF/LOCAL switch to the OFF position. This releases the brake 
and inhibits the operation of the G850 SCR Motor Driver circuits. Then the hubs are free to be loaded or 
unloaded with tape reels. If a new reel is to be mounted, unreel about a foot of tape from it over the 
guides and read/write head and wind the tape one or two revolutions onto the right reel. Turn the switch 
to either LOCAL or REMOTE as is desired for the next operation. 



3-1 



TABLE 3-1 FUNCTIONS OF CONTROLS AND INDICATORS 



Control or Indicator 



Function 



Reverse tape-motion switch (designated in 
figure 1-1 by arrow pointing to the left) 

WRITE ENABLED/WRITE LOCK switch 
WRITE ENABLED 

WRITE LOCK 



WRITE ENABLED indicator 



Address selector (or unit selector) 

1 
2 
3 
4 
5 
6 
7 
8 



OFF LINE 

REMOTE/OFF/LOCAL switch 
REMOTE 



OFF 



Provides reverse tape motion (i.e., from right to left) 
only if REMOTE/OFF/LOCAL switch is on LOCAL. 



Permits external DECtape control system to write in- 
formation on the TU55. 

Prevents the above writing. If external DECtape con- 
trol system is commanded to write on tape during the 
WRITE LOCK setting, the control initiates a selection 
error flag to notify the program. 

The WRITE LOCK setting, however, does not prevent 
tape motion when the REMOTE/OFF/LOCAL switch 
is on REMOTE. 

Lights when WRITE ENABLE/WRITE lock switch is in 
the WRITE ENABLE position. 



When set to one of the numerals (designating addresses) 
and REMOTE/OFF/LOCAL switch is on REMOTE or 
OFF, the transport is selected when the line indicated 
by the switch wiper corresponds to the computer selec- 
tion through the DECtape control. Then the trans- 
port responds to command signals from external control 
and can assert a write enabling signal to the control . 
In addition, all head channels are connected through 
the head relay to control bus information lines. 

Prevents external DEC control system from selecting 
the TU55 . 



Permits TU55 to accept command and control signals 
from the external DECtape control system; also enables 
head relay logic to connect all head channels to con- 
trol bus information lines as soon as appropriate trans- 
port is selected. 

Inhibits operation of the G850 SCR Motor Control 
Modules and releases the brakes. Power for the logic 
components comes from power supplies associated with 
the external control, and therefore the OFF position 
does not turn off the +10 and -15v power. The OFF 
position is used when loading new tape reels since it 
releases the motor hubs. The transport should be set 
to OFF when not in use. 



3-2 



TABLE 3-1 FUNCTIONS OF CONTROLS AND INDICATORS (continued) 



Control or Indicator 



Function 



LOCAL 



Permits forward and reverse tape-motion switch to 
provide tape motion in direction of arrow. Transport 
cannot be selected. 



REMOTE indicator 

Forward tape-motion switch (designated 
in figure 1-1 by arrow pointing to the 
right) 



Lights only when transport is selected by the control. 

Provides for motion in the forward direction (i.e., 
from left to right), but only when REMOTE/OFF/ 
LOCAL switch is on LOCAL. If both reverse and 
forward tape-motion switches are pressed simulta- 
neously, the forward motion takes place. 



3-3 



CHAPTER 4 
MAINTENANCE 



4.1 



EQUIPMENT REQUIRED 



Maintenance activities servicing TU55 DECtape Transports require the equipment listed in 
table 4-1 , or the equivalent; plus standard hand tools, cleansers, test cables, probes, etc. 

TABLE 4-1 RECOMMENDED MAINTENANCE EQUIPMENT 



Equipment 



Manufacturer 



Model 



Multimeter 
Oscilloscope * 



FLIP CHIP module 
extender 

Small thin-bladed 
screwdriver 

Phillips-head 
screwdrivers 

Allen-wrench set 



Triplett or Simpson 
Tektronix 

DEC 



630-MA or 260 

Series 540 or 580 
with Type CA differ- 
ential preamplifier 

W980 



All four standard 
sizes 

No. 667 



* Head gain and head skew tests require a dual-beam oscilloscope such as Tektronix Type 550 or 551 
with a high-gain differential preamplifier for each beam channel, such as Tektronix Type D. However, 
these tests are seldom necessary in the field. 



4.2 



PREVENTIVE MAINTENANCE 



The following weekly and monthly preventive maintenance schedules are recommended to 
forestall possible failures. Special emphasis is placed on cleanliness of tape handling surfaces because 
dust and oxide particles contribute to read errors. 



4.2.1 Weekly Schedule 

a. Clean entire front panel of tape deck. 

b. Clean both surfaces of tape guides and tape head using an appropriate head cleaner 
and a soft lint-free cloth. 

c. Check proper operation of motor and reel brakes before loading tape by momentarily 
pushing forward and reverse tape-motion switches on front panel. 

4-1 



4.2.2 Monthly Schedule 

This schedule should be performed on each DECtape once a month when equipment operates 
on a standard 8-hour shift and more often when daily operation exceeds one shift. Stagger the check- 
outs on individual transports evenly throughout each month. 

a. Clean the exterior and interior of the cabinet using a vacuum cleaner and clean cloths 
moistened, if necessary, in nonflammable solvent. 

b. Clean air filters at the bottom of bay using procedure given in PM section of maintenance 
manual for DECtape control system. 

c. Lubricate door hinges, casters, etc., with a light machine oil. 

d. Inspect equipment for completeness and general condition. Repaint scratched or corroded 
areas . 

e. Make sure each FLIP CHIP module is securely seated in its mounting panel connector. 

f . Run a complete exercise and diagnostic routine for each transport so that both the trans- 
port and its associated control are exercised in all possible modes and in both directions. 
Maintenance programs for this purpose are available from DEC for all computer/control/ 
transport DECtape systems. Applicable programs are listed in the maintenance manual for 
the DECtape control system. Log all errors to provide a malfunction history as an aid to 
troubleshooting. If tape is slack or bounces during exercises, perform the adjustment and 
calibration procedures in the next subsection. 

g. Rotate tapes among all transports and use the read routines of the maintenance programs 
to be sure that all transports can read tapes generated by other transports. If each transport 
operated satisfactorily instep f, any malfunctions in this step are probably due to head skew. 
Head skew can be measured by the procedures given later in the troubleshooting subsection 
but cannot be adjusted in the field. 

4.3 TAPE TENSION AND TRANSPORT STOP ADJUSTMENT 

a. Set the R303 Integrating Delay to about 70 ns. Pin D in A04 of the delay is varied 
with the aid of the trimpot mounted on the module. 

Initiation of the delay is made by pressing momentarily on either the forward or reverse 
switch when the REMOTE/OFF/LOCAL switch is on LOCAL. No tape reel is needed for 
this operation. 



4-2 



b. Mount a tape reel on the transport. Press the forward switch and watch the tape move- 
ment. The trailing torque of the left motor should be adjusted on the G850 Module A1 1 
trimpot (as shown in figure 4-1). If the torque is too great it will impede the movement at 
the tape; and if too little, flapping or loose contact with the read write head will result. 
The technician who maintains the equipment might develop a "touch" so that by pressing 
his finger over the tape at the trailing reel he can tell if the tape is too tight or loose, 
simply by the stiffness of the tape while in motion. 

c. Repeat same procedure for reverse tape movement by pressing reverse switch. This 
time the pot adjustment is done on module A12. 

d. Press forward switch for a second or two and release it; the tape action while stopping 
should be smooth. If bouncing occurs, Increase the stopping torque until bounce just 
disappears. This stop torque is maintained when the transport is not operating (which is 
most of the time) and excessive torque merely results in overheating the motor and hence 
the whole equipment. Torque adjustment is made on the appropriate pot (figure 4-1) on 
module A12. 

e. Repeat same procedure when pressing the reverse switch, watching for the stop when 
tape movement is in reverse. Adjust pot on module Al 1 . 



POT FOR 
DRAG TORQUE 
ADJUSTMENTS 




POT FOR STOP 
(OR AT REST) 
ADJUSTMENTS 



o 






G250 MODULE 



Figure 4-1 Module Adjustment Trimpots 



4.4 



HEAD OUTPUT CHECK 



This check is used to determine whether the read-head is developing the proper read signals, 
If the read-head performance is not satisfactory, the head should be replaced. No attempt should be 



4-3 



made in the field to repair or even change head position by loosening the brackets that hold it to the 
plate. Although DEC personnel are authorized to replace heads in the field, the replacement involves 
realignment and usually requires the return of the transport to DEC, Maynard. The following diagnostic 
procedure can be performed with any single-channel oscilloscope having a high-gain differential pre- 
amplifier capable of handling signals in the millivolt range over a bandwidth of to 60 kc , (Tektronix 
Type D Plug-in Unit). 

a. Mount a DEC certified tape on the TU55 Transport. Move tape manually in a forward 
direction until approximately one half of the tape is on each reel. 

b. Disconnect the 22-pin Amphenol head connector from rear of Head-Relay Module G851 
located at the extreme right of the mounting panel seen from the rear. Attach the two probes 
of the differential amplifier to pins B and C of this connector and attach the ground clip to 
D. Set the oscilloscope to sync internal, and set the vertical preamplifier to 5 mv/cm 

(0.5 mv/cm if an XT probe is used). 

An alternative method is to cause a closure of the information relays by grounding (with the 
aid of a clip) pin E of the G851 Module at location AB1 . This eliminates disconnecting the 
plug procedure, as outlined above, by making it possible to monitor the same plug points on 
the wiring panel front. The probes are now attached to pins AF and AH of the same FLIP CHIP 
socket AB1 . The gound clip is attached to pin C. 

c. Move tape forward and reverse using forward tape-motion switch and observe that the 
read- head waveform is about 10 to 12 mv peak-to-peak. 

d. Repeat step c, attaching the probes to pins F-H, P-R, U-V, and Y-Z. These signals may 
not look sinusoidal (as they do for pins B-C), but the peak-to-peak amplitude should measure 
the same as in step c. The same alternative exists here as in step b. The pin pairs to monitor 
now are: AN-AP, AV-BD, BH-BJ, and BN-BP. 

4.5 HEAD-SKEW CHECK 

Although the head-skew is not adjustable in the field, the following check should be performed 
when unusual numbers of read errors are observed on an individual transport engaged in reading tapes 
generated by several other transports. The procedure requires a dual-beam oscilloscope with two high- 
gain differential preamplifiers for each scope channel (as outlined in the equipment needed,4.1). 

a. Write a timing track on a scratch tape using one of the DECtape utility routines. 



4-4 



b. Rewind tape back onto the left reel. Dismount the left reel from the left hub and mount 
it on the right and mount the empty reel on the left hub. Thread tape over the head and onto 
the left reel. Move tape in reverse to fill up the left reel. The tape is now with its oxide 
facing up away from the head. 

c. Disconnect the 22-pin Amphenol head connector from rear of Head Relay Module G851 . 
This module is located at the extreme right of the mounting panels, seen from the rear. 

d. Connect the two upper-scope channel probes to head connector pins A and C and their 
ground clips to the chassis. Connect the two lower-scope channel probes to head connector 
pins A and D and their ground clips to the chassis. Set both channel preamps to A-B (the 
differential setting). 

e. Move tape forward by using the forward tape-motion switch. Adjust channel gain so 
that each waveform has the same peak-to-peak voltage. Sync on the upper beam and take 
a reading of the phase difference between the signal peak at pins A and D (track 10) with 
respect to the signal peak at pins A and C (track 1). Be sure to record whether the track 
10 signal leads or lags the other and the amount. Make all readings as near the center of 
the tape length as possible. Skew readings greater than 5 psec indicate possible incompati- 
bility among transports. Probably the head has become misaligned through physical damage. 
Then the transport must be returned to DEC, Maynard, for realignment. 

f. Remove all probes, reconnect the Amphenol connector to the rear of the G851 Head 
Relay Module, and rewind the tape to the original state. 

NOTE 1: It is possible here also to use the alternative method of monitoring 
the channel waveforms (see alternate method, section 4.4b) by energizing 
the relay at the G851 Module by grounding pin E. By doing so probe clips 
can be attached to the wiring panel pins at location Al . The pins are D-H 
for one probe and D-J for the other. 

NOTE 2: In some heads (manufacturer, GJM) use pin F instead of pin H on 
the FLIP CHIP socket. On the Amphenol plug at the back use pin B instead 
of pin C. 

4.6 WRITE ENABLE CIRCUIT CHECK 

a. Set the WRITE ENABLE/WRITE LOCK switch to WRITE position and check that the WRITE 
ENABLE indicator lights. Also check that a ground level is present at terminals A5L and 
A6L(C8). 



4-5 



b. Set the switch to the WRITE LOCK position and check that the WRITE ENABLE indicator 
is extinguished. Also, check that level at terminals A5L and A6L is — 3v. Check transmission 
of this level from terminal A5L to the DECtape control system. 

4.7 TROUBLESHOOTING 

The forward and reverse tape-motion switches on the front panel of the 11)55 are useful in 
checking the operation of the unit and in assuring that the tape-motion mechanism is working properly. 
It is suggested that the first step in troubleshooting should be a check of the modular logic circuits. 

For this check, the primary ac power cable should be disconnected from the plug at the back 
of the transport to prevent movement of the tape drive motors. Set the REMOTE/OFF/LOCAL switch to 
the LOCAL position. Then simulate the commands to GO FORWARD and GO REVERSE by pressing the 
appropriate switch. When the switch is released, the STOP command is initiated to energize the left 
motor shaft brake (the brake coil is energized from the — 15v supply). Under these conditions, use an 
oscilloscope or a voltmeter to compare the command signals throughout the logic circuits against those 
In table 3-1 . 

This operation is checked by monitoring the terminals of the Type G850 Modules (AT 1 and 
A12) and the Type W040 Modules (B12) with an oscilloscope of voltmeter to verify proper signal levels 
for all operating conditions of the MOTION and DIRECTION flip-flops (B08). Then inspect the motor 
hubs to check for proper operation of the brakes. This is accomplished by assuring that the proper hub 
stops when called upon to do so by the command logic (activated by operation of the front panel tape- 
motion switches). 

If the truth table cannot be verified, continue troubleshooting by signal tracing, monitoring 
the signal levels at different NAND gate inputs and outputs and working back toward the control flip- 
flops until the cause of the malfunction is found. If the truth table can be verified, restore the primary 
ac input power, install a reel of tape on the drive mechanism, and repeat the truth table verification 
procedure for proper tape movement and end stopping. If the malfunction still exists, check the 
following sources of trouble: 

a. Transformer Tl secondary is not presenting stepped down ac power to terminals U and V 
of the modules A1 1 and A12 (the Type G850 SCR Motor Driver Modules). 

b. Type G850 Modules are defective. 

c. Electromechanical system (e.g. reel motor) rather than the control logic. 



4-6 



4.8 



RECOMMENDED SPARES 



Table 4-2 lists the recommended spare parts for 11)55 Transport systems. A R-series module 
in the TU55 may be replaced by an S-series module with the same number. All items are available at 
DEC, Maynard, but may be ordered from the other firms listed. 

TABLE 4-2 RECOMMENDED SPARE PARTS 



Part 
Number 



G850 
G851 
R002* 
R303** 
SI 07* 

sin* 

S202* 

W040 

W513*** 

W701I 

MD/B570- 
0-1 1-1 -A 

8132K20 
G6V52 

8132K22 
G6V52 

8137K21 
G6V52 

7533-7 

MOT-1 

BK-0001 



Part 



SCR motor driver 

Head relay 

Diode network 

Integrating one shot 

Inverter 

Diode gate 

Dual flip-flop 

Solenoid driver 

Level amplifier 

Input network 

Rotary selector switch (address selector) 

Rocker switch (REMOTE/OFF/LOCAL) 

Rocker switch (WRITE ENABLED/LOCK) 

Rocker switch (forward and reverse tape- 
motion) (with off-nonmomentary on circuit) 

Capacitor (reel motor), 7 mfd, 300 wvdc 

Torque motor, 70-frame, SP spec 

Friction brake, FB-181-23 
DEC spec 



Manufacturer 



DEC 
DEC 
DEC 
DEC 
DEC 
DEC 
DEC 
DEC 
DEC 
DEC 
DEC 

Cutler-Hammer 

Cutler-Hammer 

Cutler-Hammer 

Sangamo 

Electric Indicator 
Co. (ELINCO) 

Megatrol 



* These modules are contained in the basic PDP-8 or the TC01 DECtape Control, so duplicate spare 
parts are not required if the TU55 is part of this system configuration. 

** This module is contained in the TC01 , so a duplicate is not required if the TU55 is used with a TC01 
DECtape Control . 

*** This module is required only if the TU55 is not used with a TC01 DECtape Control. 



4-7 



CHAPTER 5 
ENGINEERING DRAWINGS 



5.1 INTRODUCTION 

This section contains reduced copies of the engineering drawings, (see Pertinent Documents 
chapter 1) required for understanding and maintaining the Type TU55 DECtape Transport. These drawings 
are in addition to the complete set of full-size drawings forwarded with each TU55 . Only the full size 
drawings should be used by maintenance personnel for work on the units. The full-size drawings show 
variations peculiar to an individual installation. 

5.2 CIRCUIT SYMBOLS 

The block schematics of DEC equipment ore multipurpose drawings that combine signal flow, 
logical function, circuit type and physical location, wiring, and other pertinent information. Individual 
circuits are shown in block or semiblock form, using special symbols that define the circuit operation. 
These symbols are similar to those appedring in the FLIP CHIP Module Catalog but are often simplified. 
Figure 5-1 illustrates symbols used in DEC engineering drawings. 

5.3 LOGIC SIGNAL SYMBOLS 

DEC standard logic signal symbols are shown at the input of most circuits to specify the enabling 
conditions required to produce a desired output. These symbols represent either standard DEC logic levels 
or standard FLIP CHIP pulses. 

5.3.1 Logic Levels 

The standard DEC logic level is either at ground (0 to — 0.3v) or at — 3v (—2.5 to — 3.5v). 
Logic signals generally have mnemonic names which indicate the condition represented by assertion of the 

signal. An open diamond ( > ) indicates that the signal is a DEC logic level and that ground represents 

assertion; a solid diamond ( ► ) indicates that the signal is also a DEC logic level and that — 3v repre- 
sents assertion. All logic signals applied to the conditioning level inputs of diode-capacitor-diode gates 
must be present for a minimum of 400 nsec before an input pulse will trigger operation of the gate. 

5.3.2 FLIP CHIP Pulses 



Two types of pulses, R series and B series, are used in FLIP CHIP circuit operation. The pulse 
produced by R-series modules starts at — 3v, goes to ground (— 0.2v) for 100 nsec, then returns to — 3v. 
This pulse is shown in figure 5-2. 

5-1 



NON-STANDARD SIGNAL 



GROUND LEVEL PULSE 



NEGATIVE PULSE 



GROUND LEVEL 



NEGATIVE LEVEL 



oi> 



LEVEL TRANSITION USED AS A PULSE 
OR TRIGGERING ON THE LEADING EDGE 
OF A GROUND LEVEL 



-K> 



TRIGGERING ON THE TRAILING EDGE 
OF A PULSE 



•-VW- 



-15V LOAD RESISTOR CLAMPED AT -3V 




2t O 



3 — 



or 1 



2 2 

[ a] or 1 r~1 



PNP TRANSISTOR INVERTER 

1. BASE 

2. COLLECTOR 

3. EMITTER 




GROUND -LEVEL NAND, NEGATIVE-LEVEL 
NOR DIODE GATE 




GROUND-LEVEL NOR, NEGATIVE -LEVEL 
NAND DIODE GATE 



Figure 5-1 DEC Symbols 
5-2 



-y 



"7 



CAPACITOR -DIODE GATE, POSITIVE OR NEGATIVE 
INDICATED BY POLARITY OF THE INPUTS. 
1. PULSE INPUT 

2. CONDITIONING LEVEL INPUT 

3. PULSE OUTPUT 



DIODE-CAPACITOR-DIODE 
GATE 



CAPACITOR- DIODE 
GATE 




PULSE INVERTER 



1— - 




PULSE AMPLIFIER 

I. PULSE INPUT, POLARITY INDICATED 
BY INPUT SIGNAL 
2,3. TRANSFORMER -COUPLED PULSE 
OUTPUT. EITHER TERMINAL MAY 
BE GROUNDED 



1I-OI 



6 7 A 6 7 



Z 5 4 



<J— 3 



FLIP-FLOP (MOST FLIP-FLOPS HAVE ONLY SOME 
OF THE FOLLOWING): 

I. DIRECT- CLEAR INPUT 

2. GATED-CLEAR INPUT 

3. DIRECT-SET INPUT 

4. GATED-SET INPUT 

5. COMPLEMENT INPUT 

6. OUTPUT LEVEL, -3 V IF 0,OV IF 1 

7. OUTPUT LEVEL, OV IF 0, -3V IF 1 

8. CARRY PULSE OUTPUT, UPON BEING CLEARED 




DELAY (ONE -SHOT MULTIVIBRATOR) 
I. INPUT PULSE 

2. OUTPUT LEVEL, -3 V DURING DELAY 
3,4. TRANSFORMER -COUPLED PULSE 
OUTPUT. EITHER TERMINAL MAY 
BE GROUNDED 



Figure 5-1 DEC Symbols (continued) 



5-3 




400NSEC 



Figure 5-2 FLIP CHIP R-Series Pulse 



The B-series negative pulse is 2.5v in amplitude and 40 nsec in width as shown in figure 5-3 
If this pulse is applied to the base of an inverter, the inverter output will be a narrow pulse, similar in 
shape to the R-series standard pulse. The B-series positive pulse, which goes from ground to+2.5v, 
the inverse of the B-series negative pulse. 



is 



OVERSHOOT 



GND 



-2 5V 




PULSE 
pfr- WIDTH -*j 

Figure 5-3 FLIP CHIP B-Series Pulse 



5.4 



SEMICONDUCTOR SUBSTITUTION 



Standard EIA components as specified in table 5-1 can replace most DEC semiconductors used in 
modules of the TU55 DECtape Transport. Exact replacement is recommended for semiconductors not listed. 



TABLE 5-1 SEMICONDUCTOR SUBSTITUTION 



DEC 



EIA 



DEC 



EIA 



D662 
D664 
DEC 3009 
DEC 3494 



1N645 
IN 3606 
2N3009 
2N3494 



DEC 3638 
DEC 3639,-0 
DEC 3790 
MR2066 



2N3638 
2N3639 
2N3790 
1 N4003 



5-4 







efe t>*/ fi 



*'-%> 



Solid State DECtape Transport BS-D-TU55-0-2, Rev J 



5-5 





1 


2 


3 


4 


5 


6 


7 


8 


9 


10 


II 


12 




G65i 


W032 


W032 


R303 


W02T 


W023 


W023 


Rill 


W040 


R002 


G850 


G850 




READ 

write: 

HEAD 
RELAY 


INFO 
CONN 


INFO 
CONN 


STOP 

DELAY 


CMD* 


CMD* 


SWITCH 
CONN. 


ALL 
HALT 


SEL'D 
RELAY 

DRIVER 


LEFT 

BRAKE 
ENABLE 

MOTION 


LEFT 

MOTOR 

SCR 


RIGHT 
MOTOR 
SCR 




CONN 


CONN 
































RIGHT 
MOTOR 

ENABLE 








LEFT 
WOT OR 
ENABLE 


A 










SEL 
BUS 
DRIVER 




: : 




RIGHT 
MOTOR 
ENABLE 
RIGHT 
BRAKE 

ENABLE 




LEFT 
MOTOR 

ENABLE 




W70I 


Rill 


W5I3 


R202 


Rill 


Rill 


"rioY' 


W040 






REM 
FWD 


STOP 


MOTION 


LEFT RIGHT 
MOTOR MOTOR 
ENABLE ENABL£ 


LEFT 

MJTOR 

ENABLE 


LEFT 

BRAKE 

DRIVER 




STOP 

~GC~ 
REv 


GO 


SEL 




REV. 


RIGHT 
METE'R 
ENABLE 


R 


REM 
FWD 

BRAKE 
ENBL 


LEFT 
MOTOR 
ENAfcLE 


RIGHT 
MOTOR 
ENABLE 




GO 
FWD 

write" 

ENE'L 
LOCAL 

REMOTE 


FWD. 


SEL 




DIR 


RIGHT 
BRAKE 
DRIVER 




ALL 
HALT 


RiGHt 
MOTOR 
ENABLE 
LEFT 
MOTOR 
ENABLE 
WR 
ENBL 




REM 
STOP 


REM 
GO 




SEL 




WR EN 



* LOCATIONS FOR UNIT TO UNIT BUS CONNECTIONS. 



NOTES: 

I. FOR MODULE COUNT SEE PARTS LIST 
*A-PL-TU55 -0-5 



Module Utilization List MU-D-TU55-0-5 



PIN K 



I 2 3 A 5 6 7 8 9 10 II 12 






NOTES : 

I. JUMPER A#4C TO A Of 7C 



Bus Bar for TU55 WD-D-TU55-0-4 



5-7 



MALE 
AD O 



cc 



■■}<?' 



il 



BP O- 

GND AC O— 



NOTE: 

RELAYS ARE WHEELOCK 
REED, 260 SERIES 3A 
12V DC 




Relay RS-B-G851 



-x- 



Diode Cluster RS-B-R002 



5-8 




UNLESS OTHERWISE INOICATEDt 
RESISTORS ARE l/4W v 8* 
DIODES ARE 0-664 
TRANSISTOR! ARE DEC 3639B 

PRINTED CIRCUIT "REV. FOR 
DOL BOARD IS SIA 



Inverter RS-B-R107 



D664 

oo — W- 



D664 

■o — W- 



. D-662 

^03 
: L D-662 




0-664 

-M— 



0-664 

-w— 



15,000 > 7,600 



EXAMPLE DGLt 



0-664 

-N— 



Ho-662 I 
,.013 



-L. CI 
^ .01 
MFD | 



>I6A00 >7,800 



>I6,000 > 7,600 



UNLESS OTHERWISE INDICATED: 
RESISTORS ARE I/4W; 5% 
PRINTED CIRCUIT REV. FOR 
DGL BOARD IS SIB 



Diode Gate RS-B-R111 



5-9 



j[D46 j[D« 




Dual Flip-Flop RS-B-R202 




IMLEM OTHOIWK INOKATEO 
■KMTOM «W IMW.10% 
DKIOCt ME 0*962 

■TOIIt ME ' DEC MMt PARTS UtT A-*l~*Ml-0-0 



Integrating One-Shot RS-B-R303 



5-10 



do-H 




UNLESS OTHERWISE INDICATED; 
RESISTORS ARE I/4W; 10% 
DIODES ARE D-664 



Solenoid Driver RS-B-W040 



DM 




UNLESS OTHERWISE INDICATEO 
TRANSISTORS ARE DEC 2694-16 
DIODES ARE 664 
RESISTORS ARE 10,000; I/4W, 10 % 
RESISTORS ARE 1/4 W, 10% 



NOTE TO BE USED WHEN SOlIO STATE DEC TAPE TU56 IS 

CONNECTEO TO A CONTROL THAT HAS. RELAY DRIVERS. (550,351,552) 



C3j_ ?«25 

.01 -I- i 1*0 
MFD I i 2W 

6"- 



Level Amplifier RS-B-W51 3 



5-11 




DIGITAL EQUIPMENT CORPORATION □ MAYNARD , MASSACHUSETTS 

Printed in U.S.A.